The present invention relates generally to a connector and, more specifically, to an optical coupler for a single fiber optical cable.
The employment of fiber optic cables or light guides, also sometimes referred to as optical communication fibers, for the transmission of information-bearing light signals, is now an established art. Much development work has been devoted to the provision of practical low-loss glass materials and production techniques for producing glass fiber cables with protective outer claddings or jackets. The claddings make them resemble ordinary metallic-core electrical cable upon superficial external inspection. Obviously, if fiber optic cables are to be used in practical signal transmission and processing systems, practical connectors for the connection and disconnection of fiber optic cables must be provided.
Some references will now be given for background in the state of fiber optic art in general. An article entitled, "Fiber Optics," by Narinder S. Kapany, published in Scientific American, Vol. 203, pgs. 72-81, November, 1960, provides a useful background in respect to some theoretical and practical aspects of fiber optic transmission.
Of considerable relevance to the problem of developing practical fiber optic connectors, is the question of transfer efficiency at the connector. Various factors, including separation at the point of abutment, and lateral separation or axial misalignment, are among the factors effecting the light transfer efficiency at a connector. In this connection, attention is directed to the Bell System Technical Journal, Vol. 50, No. 10, December 1971, specifically to an article by D. L. Bisbee, entitled, "Measurement of Loss Due to Offset, and End Separations of Optical Fibers". Another Bell System Technical Journal article of interest appeared in Vol. 52, No. 8, October, 1973, and was entitled, "Effect of Misalignments on Coupling Efficiency on Single-Mode Optical Fiber Butt Joints," by J. S. Cook, W. L. Mammel and R. J. Grow.
Fiber optic bundles are normally utilized for only short transmission distances in fiber optic communications networks. On the other hand, fibers are used individually as optical data channels to allow transmission over many kilometers. At present, most fiber optic cables are multi-fiber bundles due to the less stringent splicing requirements, greater inherent redundancy and higher signal-to-noise ratio. The difficulty in achieving connections between single fibers which are insensitive to axial misalignment problems has created an obstacle to the use of long run single data transmission systems.
Therefore, a connector or coupler is required to eliminate lateral tolerances if low-loss connections are to be obtained in the use of single fiber optical transmission arrangements. "V" groove and metal sleeve arrangements have been used to interconnect single fibers. Reference is made to U.S. Pat. No. 3,768,146 which discloses a metal sleeve interconnection for single fibers. The problem in achieving alignment between single fibers is enhanced due to the typical lack of concentricity between the fiber core and its outside cladding or jacket. Thus, even if the optical fiber cables are perfectly aligned, the cores therein may be laterally displaced. Therefore, what is needed and constitutes the purpose of the present invention is to provide a coupling arrangement for a single optical fiber and a light emitting device, such as a second fiber or an LED, for example, which may be incorporated into a connector for practical field utilization, which is insensitive to fiber core alignment problems and problems in lack of concentricity between the core and the cladding or jacket of the optical fiber cable.
Reference is made to U.S. Pat. Nos. 3,756,688; 3,780,295; and 3,809,455 which relate to optical fiber couplers which are somewhat relevant to the present invention in that some form of optical means is utilized for directing light from a source to an optical fiber.